Modern vehicle fuel systems generally include a vapor storage canister to collect at least those vapors from the tank that form as the tank sits, often called the diurnal vapors. A vent line typically runs from a vapor pressure chamber at the top of the tank to the storage canister, and is often restricted so as not to actually encourage the formation of vapors in the tank as it sits. If, during filling of the tank, liquid is allowed to rise high enough in the tank to reach the vent line, it could conceivably reach and contaminate the adsorbent material in the canister. Therefore, it has been the practice to provide an overfill protection float internal to the tank, below the opening of the vent line into the top of the tank, which is buoyed up to block the vent line in the event of overfill.